supplement ii to the japanese pharmacopoeia fifteenth edition - NIHS

Supplement II, JP XV General Tests, Process and Apparatus 2051the desorption peak and obtain the proportion of gas volume perunit peak area.Use a nitrogen/helium mixture for a single-point determinationand several such mixtures or premixing 2 streams of gas fora multiple-point determination. Calculation is essentially thesame as for the volumetric method.A: Flow control valveB: Differential flow controllerC: On-off valveD: Gas inletE: O ring sealsF: Cold trapG: Thermal equilibration tubeH: DetectorI: Digital displayJ: Calibrating septumK: Sample cellL: Self seals quick connectionM: Short path ballastN: DetectorO: Path selection valveP: Long path ballastQ: Flow meterR: Outgassing stationS: Diffusion baffleT: VentFig. 3.02-1Schematic diagram of the dynamic flowmethod apparatus3.2 Method II: the volumetric methodIn the volumetric method (see Fig. 3.02-2), the recommendedadsorbate gas is nitrogen which is admitted into the evacuatedspace above the previously outgassed powder sample to give adefined equilibrium pressure, P, of the gas. The use of a diluentgas, such as helium, is therefore unnecessary, although heliummay be employed for other purposes, such as to measure thedead volume.Since only pure adsorbate gas, instead of a gas mixture, isemployed, interfering effects of thermal diffusion are avoided inthis method.Admit a small amount of dry nitrogen into the sample tube toprevent contamination of the clean surface, remove the sampletube, insert the stopper, and weigh it. Calculate the weight of thesample. Attach the sample tube to the volumetric apparatus.Cautiously evacuate the sample down to the specified pressure(e.g. between 2 Pa and 10 Pa). Alternately, some instrumentsoperate by evacuating to a defined rate of pressure change (e.g.less than 13 Pa/30 s) and holding for a defined period of timebefore commencing the next step.If the principle of operation of the instrument requires the determinationof the dead volume in the sample tube, for example,by the admission of a non-adsorbed gas, such as helium, thisprocedure is carried out at this point, followed by evacuation ofthe sample. The determination of dead volume may be avoidedusing difference measurements, that is, by means of referenceand sample tubes connected by a differential transducer.Raise a Dewar vessel containing liquid nitrogen at -195.8ºCup to a defined point on the sample cell. Admit a sufficientvolume of adsorbate gas to give the lowest desired relativepressure. Measure the volume adsorbed, V a . For multipointmeasurements, repeat the measurement of V a at successivelyhigher P/P 0 values. When nitrogen is used as the adsorbate gas,P/P 0 values of 0.10, 0.20, and 0.30 are often suitable.A: Vacuum gaugeB: Nitrogen reservoirC: Helium reservoirD: Vapour pressure manometerE: Vacuum airF : To cold traps and vacuum pumpsFig. 3.02-2Schematic diagram of the volumetric methodapparatus4. REFERENCE MATERIALSPeriodically verify the functioning of the apparatus using appropriatereference materials of known surface area, such asα-alumina for specific surface area determination, which shouldhave a specific surface area similar to that of the sample to beexamined.